How to make this thorny decimated effect?
Using a child object for hair particle system can give something close to what we want.

To do it, I started from a free model downloaded, then:

Added a particle system (the parameters are visible in the image) with an object as render element (a small pyramid)
Convert the particles to mesh using the convert button in the modifiers panel
Here you get individual instances of the initial pyramid. You need to select them all and use the menu &quot;object/relation/make single user&quot; to make independent instances of this pyramid
Once done, select and merge them all using AltJ
I've also added a material, and a rapidly done texture on it.

Variations can be obtained with different ways:

The amount of particles
Scale and scale randomness in the particle system setting
Scale of the particle object and its shape, of course
Add a second particle system with another shape as render object
...

Once the final mesh obtained, you can:

Resize individual pyramids inside the mesh (scale using 'individual origin' as pivot point)
Give a try at &quot;merge by distance&quot; (with a relatively big distance), which allow to link several pyramid parts

I also think that the material and textures on it are important for the final effect. Here the texture is roughly done but you may pay attention to this point if you want to go further.
The blend file below contains several attempts, so you can play with it.